Field
The present disclosure relates generally to solid state light emitters, and more particularly, to inrush energy control for solid state light emitters.
Background
Solid state light emitters, such as light emitting diodes (LEDs), are becoming the favored choice for general lighting applications over incandescent lamps and fluorescent fixtures for their lower power demand. An LED converts electrical energy to light. Light is emitted from active layers of semiconductor material sandwiched between oppositely doped layers when a voltage is applied across the doped layers. In order to use an LED chip, the chip is typically enclosed along with other LED chips in a package. In one example, the packaged device is referred to as an LED array. The LED array includes an array of LED chips mounted onto a heat conducting substrate. A layer of silicone in which phosphor particles is embedded is typically disposed over the LED chips. Electrical contact pads are provided for supplying current into the LED array and through the LED chips so that the LED chips can be made to emit light. Light emitted from the LED chips is absorbed by the phosphor particles, and is re-emitted by the phosphor particles so that the re-emitted light has a wider band of wavelengths.
As a solid state device, solid state light emitters are operated by direct current (DC) voltage. A constant current DC driver may be used as the power source to one or more solid state lighting fixtures. Conventional power control for such an arrangement includes switching AC input line voltage to the DC driver on or off, using a manual wall switch for example. For large lighting installations where remote power control of many lighting fixtures is sought from a central location, maintaining individualized control capability is desirable for flexibility of the lighting system operation. A local control circuit within each lighting fixture is needed to provide enhanced network control of a lighting system.
A local control circuit can provide independent control for each light fixture. However, switching a power supply at the load side presents a risk of inrush current damage to the light emitters when first powered up. This may occur if a filter capacitor at the output of the power supply driver keeps a residual charge after opening the switch to the load. Switching at the supply side of the driver surrenders the ability to maintain continuous power at the internal control circuit. Internal switching with inrush current protection is needed.